Process for preparing asphalt coated aggregate



p 1952 J. c. ROEDIGER PROCESS FOR PREPARING ASPHALT COATED AGGREGATE Filed July 24, 1947 F J: Iwmd r d MJ UMA w on mw Iv muzO MZO uzim uu Jose C.?oedz'3 'er Saverzbor b Clbbbrneg Patented Sept. 2, 1952 PROCESS FOR PREPARING ASPHALT COATED AGGREGATE Joseph C. Roediger, Brooklyn, N. Y., assignor to Standard Oil Development Company, a corpo- I ration of Delaware Application July 24, 1947, Serial No. 7 63,19 9

I, 'I he present invention relates to the coating of mineral aggregates with bituminous compositions. It is particularly directed to animproved process'by which a more firm and permanent bond is secured between the coatings and. the aggregates with resultant increase in the durability of the finished product. In accordance with my invention an improvement in the durability and water resistance of asphalt paving mixturesvissecured by treating mineral aggregates with alkyl halide silanes prior to coating the mineral aggregates with bituminous material.

A specific and preferred embodiment of my process comprises treating the mineral aggregate with methyl trichlorsilane prior to coating the same with a bituminous material.

f Z [t has heretofore been required to dry mineral aggregates, as, for example, crushed stone, crushed rock, sand, and soil, which are to be bonded by means of asphalt, since it is .very diffi cult to obtain a uniform coating of asphalt in the presence of water. This is especially necessarywhen the mixture is made'with a semi-solid or solid asphalt requiring high temperatures for application. 'Heretofore various additives have been used with the asphalt in order to secure satisfactory coating and bonding of wet mineral aggregates. 7 V asphalt with aliphatic organic amines in order to secure an asphalt composition having suitable coatingand bonding properties. On mixing a wet mineral aggregate with an asphalt containing noadditives, unsatisfactory coating is frequently obtained,'with the result that the mineral aggregate is only partially coated. This partially coated aggregate is easily stripped of the asphalt, especially if there is an exposure to the action of water, by a heavy rainfall for example, during Or shortly after the laying operation.

, One object of the present invention is to permit the coating of the surfaces of damp or wet aggregates with a bituminous composition in such a manner that the coating obtained is satisfactory and produces a firmly bonded mass. Another object of the invention is to prepare a paving mixture bonded with asphalt in which theasphalt coating when applied to either dry or'wet aggregate is not readily displaced or stripped when subjected to the action of water. Other objects of the invention will be readily understood from the following description of the same.

I have now discovered that improved bituminous paving mixtures may be readily prepared For example, it is known to treat- 3 Claims. (01. 106-281) by treating mineral aggregates, suchas crushed stone and the like, with an alkyl halide silane-or a mixture 'of alkyl halide silanes. A preferred embodiment'of my invention is to employ vaporizable alkyl halide si1anes,'as, for example, methyl trichlorsilane. In accordance. with a specific adaptation of my invention, I treat: a mineral aggregate with a vaporized alkyl halide silane contained in the stream of air utilizedto remove dust from the mineral aggregate in its preparation at a, crushing plant. Satisfactory silanes are, for example, methyl chlorsilane, ethyl chlorsilane, propyl chlorsilane, butyl chlorsilane, methyl bromsilane,methyliodosilane, ethyl florsilane, propyl iodosilane, butyl bromsilane, and the like. 'Mixed halide silanes'may also be used. In general, my'preferred compounds are alkyl chlo'r'silanes, the alkyl groupof which contains from one to four carbon atoms in the molecule. Monomers or polymersof these compounds may be used. A very desirable silane "comprises methyl trichlorsilane. 7

When mineral aggregates are treated in accordanceiwith my invention and exposed to the silanes, a reaction occurs at the aggregate surface between the mineral constituents and the silane- This reaction decreases the natural affinity of the aggregate for water, and increases its oil retaining properties, that is, the natural hydrop hilic character of most of the aggregate is changed and it'becomes hydrophobic. My

silane pretreatment-pf mineral aggregate renders oil or asphalt coated aggregate highly resistant to the stripping actionof water, which normally tends to displace oil or asphalt" from thesurface of untreated aggregate; Thus, paving mixtures made with road oil, flux asphalt, paving asphalt, hard asphalt-flux combinations or with cutback asphalts, show improved durability since the oil or asphalt film on the aggregate will be more firmly bondedto'silane treated aggregate and will be resistant to displacement by water under the conditions of normal service. 1

My invention generally covers the treatment of mineral aggregatesuch as crushed stone with a silane. As pointed out heretofore, it is .preferred that the silane be a vaporizable silane, as for example, methyl trichlorsilane. It is to be understood, however, that the mineral aggregate may be treated with liquid silanes having relatively low vapor pressures at normal temperatures. A particular and preferred adaptation of my process is to subject the mineral aggregate to treatment with a vaporizable silane. This is preferably: accomplished, for example, when 3 crushed stone is employed as the mineral aggregate, at the crushing plant. In normal stone crushing plant operations it is the usual procedure to blow the crushed stone with an air stream in order to reduce the amount of dust on the stone aggregate. In accordance with the preferred adaptation of my invention,-I combine with the air a sufficient quantity of a vaporized silane as, for example, methyl trichlorsilane. This air stream containing the vaporized halide silane is passed over the stone in order to remove The treating-stream V stream containing halide silane, and which has been substantially freed of dust, to the crushed stone. In this embodiment of my invention as stated;-I prefer to use methyl trichlorsilane in conjunction with the air stream. 7 Although any amount of the halide silane may be employed, in general when employing methyl trichlorsilane I prefer that the amount of methyl trichlorsilane in the air stream being used to removedust from the-crushed stone benot in excess .of about 10%. It is preferred to use the monomer of methyl trichlorsilane'alth'ough a polymer may also be used. Anypolymer having a viscosity less than 10 cell tis tokes .at 25 'C. is suitable although'm'ore volatile-polymers having a "viscosity less than 2 centistokes at 25 C. are preferable. V

In general, it-ispref-erredthat the temperature ofthe air treating "stream containing the silane be about atmospheric temperature. It is understood, however,.that. the temperature of the ,air stream may be; raised inorder to secure vaporization ofthe'jsil'ane'. However, inrg'eneral Iprefer to secure vaporization of the silane'in the air stream by atomizing .thejsame into the air stream. Other equivalent means may be employed as, for example, bubbling or difiusing the air stream through ajliquid bath of the silane being used to coat the aggregate. If this latter adaptation of my invention, be employed, the bath of silane through which the air is passed may be maintained at an elevated temperature in order to secure a relatively high vapor pressure ofthe silane and thus facilitate its vaporizat'ion in the air treating stream. My invention willfbe more clearly understood b trererenee to the drawing diagrammatically illustrating one embodiment of same. Referring specifically to the'drawing, stone or other equivcomprise any type, number, and arrangement of aggregates in zone 49. The respective mineral aggregate streams fall through the respective screens into zones 21, 3! and fit, respectively. Air is blown through zone 2!, introduced by Gil means of line22 and is withdrawn by means of line 23. The blown stone is removed from the bottom of zone 2i by conveying means 24. In accordance with the preferred adaptation of my invention, I utilize in the air stream a halide silane, preferably methyl trichlorsilane, and introduce this mixture of air and silane as described into zone 2! by. meansof line 22. In order to secure satisfactory-removal of the dust from the aggregate, the air stream containing the methyl trichlorsilane comprises an air Jet of a suitable velocity.

' I withdraw "the air-halide silane stream con-- taining dust from zone 2| by means of line 23 and pass this stream through filtering or equivalent means '25, which means is adapted to substantially completely remove the dust from said stream. ZoneZE- may comprise a bag filter or any other typeof equipment suitable for removing dust from a vaporous stream. If cloth filters are used to remove the dust, the filter will be rendered water repellant, lengthening the useful life'of the filterand aiding removal of moisture fromthe air stream: If-desired, additional removal of moisture can be "accomplished by cool ing the exit gas fromthe filter'and passing it through additional cloth filters. Theair stream, freedor dust, is then introduced'into zone 3! by means of line 26; In a similar manner to that described, the stone. brother aggregate is removed froi'h'iahe bottom n zone 3! by conveyin means'32. The airehalide 'silanestream is withdrawn from zon'ej tl; by means of line 33 and passed throughajfiltering means as, wherein dust is r-emovedx 'lhis stream is removed from zone as by means of linetsand-introduced into zone ti. Crushed aggregatesubstantially free of dust, is removedf'roni zone M by conveying means d2. The air-halide silanestream is removed froin zone H by'means of line 43, passed through filtering meansj id' and 'then; preferably recycled to smear bymeans ofline so and line 22 as described. Although; thisstream may be recycled directly rezon z1-,;I p rerer to pass the same through z ne. 50 wherein the concentration of the halide silane is raised to the desired degree.

In accordance wan this embodiment of my process, I contaotithe-smaller sized aggregate with the air stream. containing the largest con-'- centration of halide some; The middle sized ag gregate is contacted with an air stream containing an intermediate concentration of halide silane; while the largest-sized particles are com tacted with the air: stream containing the smallest'concentration of halidejsil ane. It is to be understood that the number of "segregation zones may be increased or decreased without affooting the concept and scope of my invention. It is; also tojbe understood. that the concentration of'the halide sil'anein the air-stream e'nte'ring zone 3| or '4! may be raised to the desired degree by passingaportion of the air stream from line 22 into lines 26 and 35 by means of lines 5'! and '52, respectively. It is to be understood that the rock may be wet or dry. It is also to beunderstoodthat'itln'iay bedesirable to provide'heatin'g either-of the halide silane in zone so through whichtheair stream is passed or to heatthe air stream' itself which will contain the haiid e silane. Zone 5fl rnay comprise a liquid bath of ha1ide;-silane through "which the air stream'passeshorj 'inay comprise ejection means or any'other suitable equipment for vaporizing the halide silane in the air stream.

The process ofmy invention may be further dr odn r ihaf swi e exam esi Example 1.A series of tests were conducted wherein trap rock was subjected to contact to methyl trichlorsilane and to various polymers of methyl trichlorsilane. In these tests the trap understood that all types of bituminous binding material can be employed, such as road oils, flux asphalt, paving asphalt, cutback asphalts, or hard asphalt-flux combinations. It is further rock was placed in a screen type basket and the 5 contemplated that conventional additives may basket suspended in a closed container at about be used with the asphalts. Particularly in the 75 P. which contained the methyl trichlorsilane case where liquid silanes are mixed with the vapors. In one series of tests the silane treated aggregate, improved bonding and coating results trap rock was mixed directly with asphalt, while may be obtained if asphalts are used containing in the other series of tests the silane treated trap 0 additives such as aliphatic organic amines, heavy rock was wetted with water and then mixed with metallic soaps, aluminum stearate, or zinc the asphalt. stearate. These additives are effective in supple- The pretreated trap rock was then coated with menting the silane treatment to produce, im- 6% of untreated cutback asphalt similar to the proved coating and bonding when for any reason ASTM designation D59'7-40T for rapid curing the silane treatment alone is not sufficient. cutback asphalt, type 2. Having now described my invention, I claim: The amount of coating on the treated trap rock 1 The process for the preparation of a was evaluated to determine the efliciency of the bituminous composition which comprises segrepretreatment. The asphalt coated trap rock gating a mineral aggregate into portions of difwas then exposed to air for curing periods of ferent particle sizes and treating said portions 0, 1 and 2 hours, after which the aggregate was with the vaporized monomer of methyl trichlorsubmerged in water for a period of sixteen hours. silane, portions of the mineral aggregate having The results of the s s are Summarized larger particle sizes being treated with lower conbBlOW- centrations of vaporized halide silane than portions of the mineral aggregate having smaller Methyl particle sizes and thereafter mixing said treated vamrfmm: fig X Y aggregate with an asphalt.

2. The process as defined by claim 1 wherein I. Dry Stone: the said treating of the mineral aggregate is ac- Mixing Ability 100 100 100 100 complished by contacting the aggregate with a 'h i s zhim nn 0 100 5 0 stream of air containing the vaporized methyl 1 hour curing. o 100 5 0 trichlorsilane. H W curing-m 5 0 3. The process defined by claim 2 in which the et Stone.

Mixing Ability .75 100 85 95 said stream of air containing methyl trichlorg' jgi gg 0 95 0 0 5 silane is passed through the said portions of lhour curing 0 95 0 0 mineral aggregate so as to contact the portions 2 hours wring 0 0 of smaller particle size first.

JOSEPH C. ROEDIGER. X Methyl trichlcr silane polymerized to a viscosity of f iagt h gl t rifiifii's ane polymerized to a viscosity of REFERENCES CITED Pfi per cent f aggregate urface The following references are of record in the originally coated with asphalt after mixing. fil f thi t t;

2 Stripping resistance is the per cent of aggregate surface remaining coated with asphalt after the sixteen hour UNITED STATES PATENTS period of submersion in Water.

Water does not wet these treated aggregates. Nu b r Na D t These results show that pretreatment of 2,191,295 oh e et a Feb. 20, 1940 aggregate with silane vapors improves the ability 2,258,219 ROChOW 1941 of the asphalt to coat and adhere to the 0 ,2 P no e Dec. 22, 1942 aggregate 2,386,259 Norton Oct. 9, 1945 Example 2 'I'rap rock was treated in the man- 2,415,333 Mikeska. F 1 47 ner described in Example 1, except liquid silanes 7,488 Anderson et al. Sept. 16, 7 were employed. In these series of tests the liquid 0 o a son 1948 silanes were mixed in varying percentages of 0%, 0.5% and 1% with the mineral aggregate OTHERi REFERENCES (crushed trap rock). The results of these tests Industrial 8r Engineering Chem s y, Au ust are tabulated below. 1946, p

Percent Silicone 0.0 0.5 1.0

Type MOS TypeXTypeY MCS TypeX'IypeY Dr ix n ig i'puit un. 100 100 100 100 100 100 100 a a a 22 a 2 23 ii gu fs r l'. 20 100 0 100 5 so i'iiiififiti1e 100 so 100 100 a a 3 it a 2 i8 fi gr s iir i g'i 10 100 o 25 100 0 50 Although the above tests were conducted Abstract of Papers of 111th Meeting of Ameriutilizing 6% untreated RC-2 asphalt, it is to be can Chemical Society, April 1947, pgs. 71-81. 

1. THE PROCESS FOR THE PREPARATION OF A BITUMINOUS COMPOSITION WHICH COMPRISES SEGREGATING A MINERAL AGGREGATE INTO PORTIONS OF DIFFERENT PARTICLE SIZES AND TREATING SAID PORTIONS WITH THE VAPORIZED MONOMER OF METHYL TRICHLORSILANE, PORTIONS OF THE MINERAL AGGREGATE HAVING LARGER PARTICLE SIZES BEING TREATED WITH LOWER CONCENTRATIONS OF VAPORIZED HALIDE SILANE THAN PORTIONS OF THE MINERAL AGGREGATE HAVING SMALLER PARTICLE SIZES AND THEREAFTER MIXING SAID TREATED AGGREGATE WITH AN ASPHALT. 